Constraint-based simulation is a fundamental concept used for assembly in a virtual environment. The constraints (axial, planer, etc.) are extracted from the assembly models in the CAD system and are simulated during the virtual assembly operation to represent the real world operations. In this paper, we present the analysis of combinations and order of application of axial and planar constraints used in assembly. Methods and algorithms for checking and applying the constraints in the assembly operation are provided. An object-oriented model for managing these constraints in the assembly operation is discussed.